2016/10/14. YU Xiangyu

Transcription

1 2016/10/14 YU Xiangyu

2

3 Frequency and Spectrum Types of Waves Propagation Model Free-Space Propagation Path Loss Fading: Slow Fading / Fast Fading Doppler Shift Delay Spread

4 FIGURE Electromagnetic frequency spectrum. Wayne Tomasi Electronic Communications Systems, Fourth Edition

5 Tomasi Advanced Electronic Communications Systems, 6e FIGURE Electromagnetic wavelength spectrum

6 Schiller P26 Frequency and wave length = c/f wave length, speed of light c 3x10 8 m/s, frequency f twisted pair coax cable optical transmission 1 Mm 300 Hz 10 km 30 khz 100 m 3 MHz 1 m 300 MHz 10 mm 30 GHz 100 m 3 THz 1 m 300 THz VL F LF M F HF VHF UHF SHF EHF infrared visible UV light

7 Frequency Name Typical application band (khz) 3 30 Very low frequency Long-distance navigation, (VLF) Underwater comm. Sonar Low frequency Navigation, underwater comm. (LF) radio beaconing Medium frequency Broadcasting, maritime comm. (MF) direction-finding, distress calling, coast guard Fan P10-11

8 Frequency Name Typical application band (MHz) 3 30 High frequency Long-distance broadcasting, telegraph, (HF) telephone, fax, search and lifesaving, comm. between aircrafts & ships, and between ship & coast, amateur radio Very high frequency TV, FM broadcasting, land traffic, air (VHF) traffic, control, taxi, police, avigation, aircraft communication Ultra high frequency TV, cellular phone network, microwave (UHF) link,, radio sounding, navigation, satellite communication, GPS, surveillance radar, radio altimeter Fan P11

9 Frequency Name Typical application band (GHz) 3 30 Super high frequency Satellite comm., radio altimeter, (SHF) microwave link, aircraft radar, meteorological radar, public land vehicle communication Extremely high Radar landing system, satellite frequency (EHF) comm., vehicle comm., railway traffic Submillimeter wave Experiment, not designated (0.1 1 mm) Fan P11

10 Frequency Name Typical application band (THz) Infrared (7 0.7 m) Optical communication Visible light ( m) Optical communication Ultraviolet Optical communication ( m) Note: khz = 10 3 Hz, MHz = 10 6 Hz, GHz = 10 9 Hz, THz = Hz, mm = 10-3 m, m = 10-6 m Fan P11

11 VHF-/UHF-ranges for mobile radio simple, small antenna for cars deterministic propagation characteristics, reliable connections SHF and higher for directed radio links, satellite communication small antenna, beam forming large bandwidth available Wireless LANs use frequencies in UHF to SHF range some systems planned up to EHF limitations due to absorption by, e.g., water (dielectric heating, see microwave oven) weather dependent fading, signal loss caused by heavy rainfall etc. Schiller P26-27

12 Examples Europe USA Japan Cellular networks GSM , , , UMTS , LTE , , Cordless phones CT , CT DECT AMPS, TDMA, CDMA, GSM , TDMA, CDMA, GSM, UMTS , PACS , PACS-UB PDC, FOMA , PDC , FOMA , PHS JCT Wireless LANs b/g b/g b g Other RF systems 27, 128, 418, 433, , , 868 In general: ITU-R holds auctions for new frequencies, manages frequency bands worldwide (WRC, World Radio Conferences); 3GPP specific: see e.g. 3GPP TS V ( ) Schiller P28-29

13 Tomasi Advanced Electronic Communications Systems, 6e TABLE Microwave Radio-Frequency Assignments

14 Classification Band Initials Frequency Range Characteristics Extremely low ELF < 300 Hz Infra low ILF 300 Hz - 3 khz Ground wave Very low VLF 3 khz - 30 khz Low LF 30 khz khz Medium MF 300 khz - 3 MHz Ground/Shy wave High HF 3 MHz - 30 MHz Sky wave Very high VHF 30 MHz MHz Ultra high UHF 300 MHz - 3 GHz Super high SHF 3 GHz - 30 GHz Space wave Extremely high EHF 30 GHz GHz Tremendously high THF 300 GHz GHz Agrawal P33

15 Ionosphere ( km) Mesosphere (50-80 km) Space wave Ground wave Earth Stratosphere (12-50 km) Troposphere (0-12 km) Agrawal P33

16 Ground-wave propagation Sky-wave propagation Line-of-sight propagation Figure Propagation of radio frequencies. Couch P41 Stallings P101

17 Tomasi Advanced Electronic Communications Systems, 6e FIGURE Microwave propagation paths

18 Follows contour of the earth Can Propagate considerable distances hundreds to thousands of km Frequencies up to 2 MHz Diffraction Example AM radio Fan P11-12 Stallings P

19 Signal reflected from ionized layer of atmosphere back down to earth Signal can travel a number of hops, back and forth between ionosphere(60 ~ 400 km) and earth s surface One hop max. propagation distance:4000 km Propagation distance by multi-hops: >10000 km Reflection effect caused by refraction Frequency:2 ~ 30 MHz Examples Amateur radio CB(Citizens Band) radio Stallings P

20 Wayne Tomasi Electronic Communications Systems, Fourth Edition FIGURE Critical angle

21 D layer: 60 ~ 80 km E layer: 100 ~ 120 km F layer: 150 ~ 400 km F1 layer: 140 ~ 200 km F2 layer: 250 ~ 400 km At night: D layer: disappears F1 layer: disappears (Or, F1 and F2 are combined as F layer)

22 Wayne Tomasi Electronic Communications Systems, Fourth Edition FIGURE Ionospheric layers

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24 Transmitting and receiving antennas must be within line of sight Satellite communication signal above 30 MHz not reflected by ionosphere Ground communication antennas within effective line of site due to refraction Refraction bending of microwaves by the atmosphere Velocity of electromagnetic wave is a function of the density of the medium When wave changes medium, speed changes Wave bends at the boundary between mediums Stallings P

25 d r ( r h) d 2rh h d h 2rh 2rh Couch P43

26 Optical line of sight d h Effective, or radio, line of sight d h d = distance between antenna and horizon (km) h = antenna height (m) K = adjustment factor to account for refraction, rule of thumb K = 4/3 Stallings P

27 FIGURE Space waves and radio horizon Wayne Tomasi Electronic Communications Systems, Fourth Edition Stallings P103

28 Maximum distance between two antennas for LOS propagation: h 1 = height of antenna one h 2 = height of antenna two 3.57 h h 1 2 Stallings P105

29 My result : 101km

30 Tomasi Advanced Electronic Communications Systems, 6e FIGURE Microwave radio communications link

31 Transmission range communication possible low error rate Detection range detection of the signal possible no communication possible Interference range signal may not be detected sender transmission detection interference signal adds to the background noise Warning: figure misleading bizarre shaped, timevarying ranges in reality! distance Schiller P35-36

32 Propagation in free space always like light (straight line) Receiving power proportional to 1/d² in vacuum much more attenuation in real environments, e.g., d 3.5 d 4 (d = distance between sender and receiver) Receiving power additionally influenced by fading (frequency dependent) shadowing reflection at large obstacles refraction depending on the density of a medium scattering at small obstacles diffraction at edges shadowing reflection refraction scattering diffraction Schiller P37-39

33 Attenuation and attenuation distortion Free space loss Noise Atmospheric absorption Multipath Refraction Thermal noise Stallings P

34 Strength of signal falls off with distance over transmission medium Attenuation factors for unguided media: Received signal must have sufficient strength so that circuitry in the receiver can interpret the signal Signal must maintain a level sufficiently higher than noise to be received without error Attenuation is greater at higher frequencies, causing distortion Stallings P106

35 Attenuation (db/km) Vapor Oxygen Frequency (GHz) (a) Attenuation of oxygen & vapor(concentration 7.5 g/m 3 ) Attenuation (db/km) Rainfall rate Frequency (GHz) (b) Attenuation of rainfall Fan P14

36 The received signal power: GtGr Pt L where P r is the received power, P t is the transmitting power, G r is the receiver antenna gain, G t is the transmitter antenna gain, L is the propagation loss in the channel, i.e., P r L = L P L S L F Fast fading Slow fading Path loss Agrawal P38

37 If a radio channel s propagating characteristics are not specified, one usually infers that the signal attenuation versus distance behaves as if propagation takes place over ideal free space. The model of free space treats the region between the transmit and receive antennas as being free of all objects that might absorb or reflect radio frequency (RF) energy. It also assumes that, within this region, the atmosphere behaves as a perfectly uniform and nonabsorbing medium. Sklar P946

38 Furthermore, the earth is treated as being infinitely far away from the propagating signal (or, equivalently, as having a reflection coefficient that is negligible). Basically, in this idealized free-space model, the attenuation of RF energy between the transmitter and receiver behaves according to an inverse-square law. The received power expressed in terms of transmitted power is attenuated by a factor, where this factor is called path loss or free space loss. Sklar P946

39 Path Loss: The signal strength decays exponentially with distance d between transmitter and receiver; The loss could be proportional to somewhere between d 2 and d 4 depending on the environment. Definition of path loss L P : L P Pt P Path Loss in Free-space: L PF r, ( db) log fc( MHz ) 20log 10 where f c is the carrier frequency. d( 10 km ), This shows greater the f c, more is the loss. Agrawal P36

40 When the receiving antenna is isotropic, this factor is expressed as where d is the distance between the transmitter and the receiver, and is the wavelength of the propagating signal. For this case of idealized propagation, received signal power is very predictable. For most practical channels, where signal propagation takes place in the atmosphere and near the ground, the free-space propagation model is inadequate to describe the channel behavior and predict system performance. Sklar P946

41 Sklar P251

42 h b h m Transmitter Distance d Receiver The received signal power at distance d: P r AeGtP 2 4 d t where P t is transmitting power, A e is effective area, and G t is the transmitting antenna gain. Assuming that the radiated power is uniformly distributed over the surface of the sphere. Agrawal P35-36

43 Antenna gain Power output, in a particular direction, compared to that produced in any direction by a perfect omnidirectional antenna (isotropic antenna) Effective area Related to physical size and shape of antenna Stallings P98-99

44 Relationship between antenna gain and effective area G 4 A e 2 G = antenna gain A e = effective area f = carrier frequency c = speed of light (» m/s) = carrier wavelength 4 f c 2 2 A e 2 A R G R 4 Stallings P100

45 Free space loss, ideal isotropic antenna P t P r 2 4 d 4 fd P t = signal power at transmitting antenna P r = signal power at receiving antenna = carrier wavelength d = propagation distance between antennas c = speed of light (» m/s) where d and are in the same units (e.g., meters) 2 c 2 2 H. T. Friis, "A note on a simple transmission formula," Proc. IRE, vol. 34, pp Stallings P

46 Free space loss equation can be recast: L db 10log Pt P r 20log 4 d 20log d db 20log 4 fd 20log 20log c f 20log d db Stallings P107

47 Free space loss accounting for gain of other antennas P t P r d d cd G G r G t = gain of transmitting antenna G r = gain of receiving antenna A t = effective area of transmitting antenna A r = effective area of receiving antenna t 2 A r A t f 2 A r 2 A t Stallings P107

48 Free space loss accounting for gain of other antennas can be recast as L db 20log d 10log A A 20log t r f 20log d 10log A t A dB 20log r Stallings P107

49 Path Loss in Free-space 130 Path Loss Lf (db) fc=150mhz fc=200mhz fc=400mhz fc=800mhz fc=1000mhz fc=1500mhz Distance d (km) Agrawal P40

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53 Simplest Formula: L p = A d α where A and α: propagation constants d : distance between transmitter and receiver α : value of 3 ~ 4 in typical urban area Agrawal P39

54 Path loss in decreasing order: Urban area (large city) Urban area (medium and small city) Suburban area Open area Agrawal P39-40

55 h b =200m, h m =2m Okamura, Y. a kol.: Field Strength and its Variability in VHF and UHF Land-Mobile Radio Service. Rev. Elec. Comm. Lab. No.9-10pp , 1968.

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57 Urban area: L PU where h m ( db) log ( m) Suburban area: Open area: L PO L PS ( MHz ) 13.82log log h ( m) log d( km) b f c 1.1log 10 fc( MHz ) 0.7 h m( m) 1.56log 10 fc( MHz ) 0.8, log h m for f MHz m( ) 1.1, c 200, for log 11.75h ( m) 4.97, for f 400MHz 10 ( db) L PU m ( db) 2 log 10 2 fc 10 c ( MHz ) h b ( m) h m ( m) small & medium city for l arg e city 2 f ( MHz ) 18.33log f ( MHz ) ( db) LPU ( db) 4.78 log c c Agrawal P39-40

58 Path Loss in Urban Area in Large City Path Loss Lpu (db) Distance d (km) fc=200mhz fc=400mhz fc=800mhz fc=1000mhz fc=1500mhz fc=150mhz Agrawal P40

59 Path Loss in Urban Area for Small & Medium Cities Path Loss Lpu (db) Distance d (km) fc=150mhz fc=200mhz fc=400mhz fc=800mhz fc=1000mhz fc=1500mhz Agrawal P40

60 Path Loss in Suburban Area Path Loss Lps (db) Distance d (km) fc=150mhz fc=200mhz fc=400mhz fc=800mhz fc=1000mhz fc=1500mhz Agrawal P40

61 Path Loss in Open Area Path Loss Lpo (db) fc=150mhz fc=200mhz fc=400mhz fc=800mhz fc=1000mhz fc=1500mhz Distance d (km) Agrawal P40

62 Rappaport P152

63 % Code for Simulation Of OKUMURA Model % Code By:- Debaraj Rana % mail- debaraj.rana@ymail.com % Dept. Of Electronics & Telecom. Engg %% VSSUT, Burla,ORISSA clc; clear all; close all; Hte=30:1:100; % Base Station Antenna Height Hre=input('Enter the receiver antenna height 3m<hre<10m : '); % Mobile Antenna Height d =input('enter distance from base station 1Km<d<100Km : '); % Distance 30 Km f=input('enter the frequency 150Mhz<f<1920Mhz : '); c=3*10^8; lamda=(c)/(f*10^6); Lf = 10*log((lamda^2)/((4*pi)^2)*d^2); % Free Space Propagation Loss Amu = 35; % Median Attenuation Relative to Free Space (900 MHz and 30 Km) Garea = 9; % Gain due to the Type of Environment (Suburban Area) Ghte = 20*log(Hte/200); % Base Station Antenna Height Gain Factor if(hre>3) Ghre = 20*log(Hre/3); else Ghre = 10*log(Hre/3); end % Propagation Path Loss L50 = Lf+Amu-Ghte-Ghre-Garea; display('propagation pathloss is : '); disp(l50); plot(hte,l50,'linewidth',1.5); title('okumura Model Analysis'); xlabel('transmitter antenna Height (Km)'); ylabel('propagation Path loss(db) at 50 Km'); grid on; eexchange/28423-okumura-modelsimulation/content/okumura.m

64 Rappaport P139

65 J. Walfisch, H. L. Bertoni, "A theoretical model of UHF propagation in urban environments," IEEE Trans. on Antennas and Propagation, vol. 36, no. 12, pp , Dec Rappaport P155

66 Intermodulation noise occurs if signals with different frequencies share the same medium Interference caused by a signal produced at a frequency that is the sum or difference of original frequencies Crosstalk unwanted coupling between signal paths Impulse noise irregular pulses or noise spikes Short duration and of relatively high amplitude Caused by external electromagnetic disturbances, or faults and flaws in the communications system Stallings P110

67 Ratio of signal energy per bit to noise power density per Hertz E b S / R S N0 N0 ktr The bit error rate for digital data is a function of E b /N 0 Given a value for E b /N 0 to achieve a desired error rate, parameters of this formula can be selected As bit rate R increases, transmitted signal power must increase to maintain required E b /N 0 Stallings P111

68 Atmospheric absorption water vapor and oxygen contribute to attenuation Multipath obstacles reflect signals so that multiple copies with varying delays are received Refraction bending of radio waves as they propagate through the atmosphere Stallings P

69 Tomasi Advanced Electronic Communications Systems, 6e FIGURE Median duration of fast fading

70 Signal can take many different paths between sender and receiver due to reflection, scattering, diffraction LOS pulses multipath pulses signal at sender LOS (line-of-sight) Time dispersion: signal is dispersed over time signal at receiver interference with neighbor symbols, Inter Symbol Interference (ISI) The signal reaches a receiver directly and phase shifted distorted signal depending on the phases of the different parts Schiller P39

71 Multiple copies of a signal may arrive at different phases If phases add destructively, the signal level relative to noise declines, making detection more difficult Intersymbol interference (ISI) One or more delayed copies of a pulse may arrive at the same time as the primary pulse for a subsequent bit Stallings P116

72 Stallings P115

73 Figure Illustrating the mechanism of radio propagation in urban areas. (From Parsons, 1992, with permission.) Haykin P532

74 Reflection - occurs when signal encounters a surface that is large relative to the wavelength of the signal Diffraction - occurs at the edge of an impenetrable body that is large compared to wavelength of radio wave Scattering occurs when incoming signal hits an object whose size in the order of the wavelength of the signal or less Stallings P

75 Reflection Propagation wave impinges on an object which is large as compared to wavelength - e.g., the surface of the Earth, buildings, walls, etc. Diffraction Radio path between transmitter and receiver obstructed by surface with sharp irregular edges Waves bend around the obstacle, even when LOS (line of sight) does not exist Scattering Objects smaller than the wavelength of the propagation wave - e.g. foliage, street signs, lamp posts Agrawal P34-35

76 Building STOP Scattered h b Diffracted Signal Reflected Signal h m Transmitter d Receiver Agrawal P35

77 Rappaport P121

78 Rappaport P122

79 Rappaport P128

80 Rappaport P129

81 Figure 4.12 Illustration of Fresnel zones for different knife-edge diffraction scenarios. Rappaport P130

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84 Ionosphere scattering Frequency: 30 ~ 60 MHz Troposphere scattering Frequency: 100 ~ 4000 MHz Meteor-tail scattering Frequency: 30 ~ 100 MHz Transmitting antenna Earth Figure Troposphere scattering communication Effective scattering region Receiving antenna Ground Figure Meteor-tail scattering communication Fan P15

85 Channel characteristics change over time and location signal paths change different delay variations of different signal parts different phases of signal parts quick changes in the power received (short term fading) Additional changes in distance to sender obstacles further away slow changes in the average power received (long term fading) power short term fading long term fading t Schiller P40

86 Fast fading Slow fading Flat fading Selective fading Rayleigh fading Rician fading Stallings P

87 Fast Fading (Short-term fading) Slow Fading (Long-term fading) Signal Strength (db) Path Loss Distance

88 Figure Small-scale and large-scale fading. Rappaport P106

89 Slow fading is caused by movement over distances large enough to produce gross variations in the overall path between transmitter and receiver. The long-term variation in the mean level is known as slow fading (shadowing or lognormal fading). This fading caused by shadowing. Agrawal P41

90 Shadowing: Often there are millions of tiny obstructions in the channel, such as water droplets if it is raining or the individual leaves of trees. Because it is too cumbersome to take into account all the obstructions in the channel, these effects are typically lumped together into a random power loss. Log-normal distribution: - The pdf of the received signal level is given in decibels by p M 1 2 e 2 M M 2 where M is the true received signal level m in decibels, i.e., 10log 10 m, M is the area average signal level, i.e., the mean of M, is the standard deviation in decibels 2, Agrawal P42

91 2 p(m) M M The pdf of the received signal level Agrawal P42

92 The signal from the transmitter may be reflected from objects such as hills, buildings, or vehicles. Fast fading is due to scattering of the signal by object near transmitter. When MS far from BS, the envelope distribution of received signal is Rayleigh distribution with b=0. The pdf is where is the standard deviation, r is the envelope of fading signal, b is the amplitude of direct signal, and I 0 is the zero order Basel Function. Middle value r m of envelope signal within sample range to be satisfied by p r 2 2 r e I ), r 0 We have r m = r 2 b 2 br 0( 2 P( r rm) 0.5. Agrawal P43

93 P(r) = =2 0.2 = The pdf of the envelope variation r Agrawal P43

94 Rappaport P211

95 When MS is far from BS, the envelope distribution of received signal is called a Rician distribution. The pdf is p r 2 2 r e I, r 0 2 r 2 2 where is the standard deviation, I 0 (x) is the zero-order Bessel function of the first kind, is the amplitude of the direct signal 0 r Agrawal P44

96 Pdf p(r) b= 0 (Rayleigh) b = 1 b = 2 b = = The pdf of the envelope variation 4 r 6 8 r Rappaport P214 Agrawal P45

97 Level Crossing Rate: Average number of times per second that the signal envelope crosses the level in positive going direction. Fading Rate: Number of times signal envelope crosses middle value in positive going direction per unit time. Depth of Fading: Ratio of mean square value and minimum value of fading signal. Fading Duration: Time for which signal is below given threshold. Agrawal P46-47

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99 Doppler Effect: When a wave source and a receiver are moving towards each other, the frequency of the received signal will not be the same as the source. When they are moving toward each other, the frequency of the received signal is higher than the source. When they are opposing each other, the frequency decreases. Thus, the frequency of the received signal is f R f C where f C is the frequency of source carrier, f D is the Doppler frequency. Doppler Shift in frequency: f D where v is the moving speed, is the wavelength of carrier. f D v cos Signal MS Moving speed v Agrawal P48-49

100 RappaportP180

101 Rappaport P219

102 Rappaport P219

103 Signal strength Different moving speed V 1 V 2 V 3 V 4 Time Agrawal P48

104 When a signal propagates from a transmitter to a receiver, signal suffers one or more reflections. This forces signal to follow different paths. Each path has different path length, so the time of arrival for each path is different. This effect which spreads out the signal is called Delay Spread. Agrawal P50

105 Signal Strength The signals from close by reflectors The signals from intermediate reflectors The signals from far away reflectors Delay Agrawal P50

106 Transmission signal 1 1 Time 0 Received signal (short delay) Time Propagation time Received signal (long delay) Delayed signals Time Agrawal P51

107 Caused by time delayed multipath signals Has impact on the burst error rate of channel Second multipath is delayed and is received during next symbol For low bit-error-rate (BER) R 1 2 d R (digital transmission rate) limited by delay spread d. Agrawal P51

108 Coherence bandwidth Bc: Represents correlation between two fading signal envelopes at frequencies f1 and f2. Is a function of delay spread. Two frequencies that are larger than coherence bandwidth fade independently. Concept useful in diversity reception Multiple copies of the same message are sent using different frequencies. Agrawal P52

109 Cells having the same frequency interfere with each other. r d is the desired signal r u is the interfering undesired signal b is the protection ratio for which r d br u (so that the signals interfere the least) If P(r d br u ) is the probability that r d br u, Cochannel probability P co = P(r d br u ) Agrawal P52-53

110 Tomasi Advanced Electronic Communications Systems, 6e FIGURE Co-channel interference

111 Tomasi Advanced Electronic Communications Systems, 6e FIGURE Adjacent-channel interference

112 Forward error correction Adaptive equalization Diversity techniques Stallings P

113 Transmitter adds error-correcting code to data block Code is a function of the data bits Receiver calculates error-correcting code from incoming data bits If calculated code matches incoming code, no error occurred If error-correcting codes don t match, receiver attempts to determine bits in error and correct Stallings P

114 Can be applied to transmissions that carry analog or digital information Analog voice or video Digital data, digitized voice or video Used to combat intersymbol interference Involves gathering dispersed symbol energy back into its original time interval Techniques Lumped analog circuits Sophisticated digital signal processing algorithms Stallings P120

115 Diversity is based on the fact that individual channels experience independent fading events Space diversity techniques involving physical transmission path Frequency diversity techniques where the signal is spread out over a larger frequency bandwidth or carried on multiple frequency carriers Time diversity techniques aimed at spreading the data out over time Stallings P

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117 Frequency and Spectrum Types of Waves Free-Space Propagation Path Loss Propagation Model Fading Doppler Shift Delay Spread

118 Stalling s book P

119